Arc chute



D. R. BOYD May 12, 1970 ARC CHUTE 2 SheefS-Sheet'l Filed Dec. 25, 1968 D. R. BOYD May 12, 1970 ARC CHUTE 2 Sheets-Sheet 2 Filed Dec. 25, 1968 United States Patent O 3,511,950 ARC CHUTE Donald R. Boyd, Waukesha, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis. Filed Dec. 23, 1968, Ser. No. 786,325 Int. Cl. H01h 33/08, 33/18 US. Cl. 200144 10 Claims ABSTRACT OF THE DISCLOSURE This invention relates to are extinguishing devices and more particularly to arc chutes for interrupting uni-directional currents.

An object of the invention is to provide an improved arc extinguishing chute for a direct current contactor which is readily removed from the contactor and has almost double the interrupting capacity of known are chutes of comparable size.

The problem of interruption is more difiicult with unidirectional currents than with alternating currents since direct current does not periodically pass through zero. Arc extinguishing chutes for direct current are therefore subject to heavy duty. Vaporized metal in the arc stream tends to maintain and stabilize the arc, and since the metallic content of the arc stream is dependent upon metal derived from the arc runners, it is desirable that the ends of the arc in contact with the arc runners, termed arc roots, be kept moving continuously in order to avoid high heat concentration and high vaporizing action on the arc runners. Further, if the arc roots remain stationary as the arc is lengthened, re-ignition of the arc frequently occurs in the short path between the arc roots because of the high voltage gradient in this vicinity, and further the arc runners quickly erode and melt at the points of high heat concentration where the static arc roots contact the arc runners.

Another object of the invention is to provide an improved arc extinguishing chute for unidirectional currents which, although compact and relatively small, has high interrupting capacity and wherein the arc roots are continuously moved outward as the arc is lengthened so that the vaporizing action of the are on the arc runners is minimized.

These and other objects and advantages of the invention will be more readily apparent from the following detailed description when considered in conjunction with the accompanying drawing wherein:

FIG. 1 is an elevation view of a direct current contactor assembled with the arc extinguishing chute of the invention, one wall of the arc chute being removed to illustrate the internal construction;

FIG. 2 is a view taken at right angles to FIG. 1 with a portion of the arc chute cut away to facilitate illustration of the components of the contactor;

FIGS. 3 and 4 are views of the two halves of the arc chute housing opened and laid back to illustrate the internal construction, the arc splitter plate being omitted;

FIG. 5 is a view through the arc chute along line VV of FIG. 3; and

FIG. 6 is a view along line VI-VI of FIG. 4.

An embodiment of the invention is shown in FIGS. 1

and 2 as applied to a direct current contactor 10. Since the contactor 10 itself forms no part of the present invention, only such components of the contactor 10 are shown and described as are pertinent to an understanding of the application of the arc chute of the invention. The contactor 10 has a U-shaped ferromagnetic frame 11 which embraces a cylindrical electrical operating coil 12 wound in surrounding relation to a ferromagnetic core 14 extending axially of coil 12. A ferromagnetic armature 16 pivotally connected to one leg 17 of U-shaped frame 11 is pulled against the other leg 18 of frame 11 when coil 12 is energized. Armature 16 is preferably split into two parts 19 and 20 to create a high reluctance path between the two parts in the manner disclosed in U.S. Pat. No. 3,238,326 to Robert J. Frey having the same assignee as this invention.

The contactor movable contact 21 is rigidly secured by screws to a rectangular-in-cross section bus bar conductor 22 mounted on armature 16. A U-shaped clamping plate 23 fits over bus bar conductor 22 and has laterally projecting ears 24. An insulating member 25 is disposed between conductor 22 and armature 16, and headed pins 26 extend through clearance holes in armature 16 and in the ears 24 of clamping plate 23. Springs 27 surrounding pins 26 react between the ears 24 and snap rings affixed to the end of pins 26 to mount conductor 22 on armature 16, and springs 27 are compressed after the contactor stationary and movable contacts 49 and 21 engage, when armature 16 is attracted to frame 11, and provide part the restoring force which returns armature 16 to its open position.

One end of a pair of flexible conductors the load current which the contactor interrupts is crimped within a U-shaped opening 29 at the end of bus bar conductor 22 opposite movable contact 21. The opposite ends of the flexible conductors 28 are clamped between a flange 30 on an interlock support frame 31 and a metallic terminal block 32 by means of screws 33. Terminal block 32 may be aflixed to frame 11 by screws 34, and a connector 35 crimped to a lead 36 from a source of electrical current may be fastened to terminal block 32 by screws 37.

Frame 11 is aflixed to an insulating base 39 which may be mounted on a switch panel by bolts (not shown) received within U-shaped openings 40 in side flanges 41 integral with base 39. One end of bus bar conductor 46 secured by screws to insulating base 39 terminates at an oblique angle and protrudes into the opening in a generally V-shaped contactor stationary contact 49 that has limited rocking movement about bus bar conductor 46. One leg 50 of V-shaped stationary contact 49 is disposed between bus bar conductor 46 and base 39 and has a plurality of spring-receiving recesses which retain coil wiping springs 51 that are compressed against base 39 when the movable and stationary contacts 21 and 49 are engaged and provide wiping action between these contacts upon separation.

A magnetic blowout coil 54 mounted on insulating base 39 has a plurality of helical turns 55 of heavy copper strap surrounding a ferromagnetic core 56. The copper strap at one end of blowout coil 54 is electrically connected to bus bar conductor 46 by screws 58, and the other end of blowout coil 54 terminates in a connector plate 59 having threaded terminal means 60 extending therethrough adapted to secure a conductor from an electrical load. Ferromagnetic flux-carrying pole pieces 61 abut against the ends of magnetic core 56 and extend radially beyond the blowout coil turns 55 and are adapted to engage ferromagnetic pole piece plates 62 of the arc chute of the invention.

28 that carry The legs of a U-shaped ferromagnetic yoke 64 are secured to the two halves 19 and 20 of armature 16 so that yoke 64 embraces flexible conductors 28 to form a pair of closed, low reluctance magnetic flux paths in surrounding relation to the members carrying load current. Each such flux path includes yoke 64, one half 19 or 20 of armature 16, the adjacent leg 17 or 18 of frame 11 and through frame 11 to the other leg 17 or 18 thereof, the other half 19 or 20 of armature 16 and back to the yoke 64. Load current flowing through flexible conductors 28 induces magnetic flux in both such magnetic paths, including yoke 64 and frame 11, which result in forces tending to hold armature 16 in engagement with frame 11 even after coil 12 is de-energized. A mechanically operated interlock 70 for auxiliary circuits includes an insulating casing 71 mounted by screws on the generally L-shaped metallic support bracket 31 having one end 72 supported from contactor base 39 and the flange 30 at its opposite end secured to terminal block 32. Interlock 70 is actuated by reciprocation of an elongated operating member 74 slidably mounted within casing 71. The ends of a U-shaped interlock actuating member 76 are secured to armature 16, and the cross-piece of member 76 is disposed adjacent operating member 74 and moves it longitudinally to operate the interlock 70 when armature 16 is attracted to frame 11. Armature restoring springs 77 disposed between interlock actuating member 76 and protruding cars 78 on support bracket 31 are compressed when armature 16 is attracted to frame 11 and urge armature 16 to its open position wherein the contactor stationary and movable contacts 49 and 21 are separated.

The arc chute of the invention has a housing 80 formed by a pair of abutting hollow side members 81 and 82. Side member 81 has peripheral rims 83 adjacent a pair of opposite edges thereof; side member 82 has peripheral rims 84 adjacent a pair of opposite edges thereof; and side members 81 and 82 are held with their open sides facing each other and with rims 83 and 84 abutting by a plurality of screws 85. Side members 81 and 82 are preferably molded of a gas evolving insulating material and may be of a phosphoric acid-bonded asbestos material. Housing 80 has a pair of laterally extending, elongated guide flanges 86 of L-shaped cross section adapted to slide within complementary grooves 88 (see FIG. 2) in the contactor base 39 to mount arc chute housing 80 on base 39. At the end adjacent contactor 10, the side members 81 and 82 are spaced apart to define an arcing compartment 89 which embraces the stationary contact 49 and movable contact 21 when the arc chute is assembled on contactor 10. The ferromagnetic pole piece plates 62 secured to the exterior of side members 81 and 82 engage the pole pieces 61 of the blowout coil 54 and generate a magnetic field therebetween within the housing 80 in a direction transverse to the side members 81 and 82.

An arc splitter plate 92 of suitable are resistant insulating material is disposed within housing 80 and divides it into two narrow side-by-side arcing chambers 93 and 94 parallel to the plane of movement of contact 21. Chamber 93 is formed between arc splitter plate 92 and side member 81, and arc chamber 94 is formed between plate 92 and side member 82.

Two elongated metallic arc runners 97 and 98 and a V-shaped metallic bridging electrode 99 disposed within housing 80 form a first pair of diverging electrodes for lengthening and extinguishing an arc segment 'within arc chamber 93 and a second pair of diverging electrodes for lengthening and extinguishing an arc segment within arc chamber 94. Elongated straight grooves 101 and 102 are molded on the interior of side member 81 adjacent rims 83. A pair of straight elongated grooves 103 and 104 are molded on the interior of side member 82 adjacent one rim 84 and an elongated, partially curved groove 105 is molded in side member 82 adjacent the other rim 84. Are runner 97 has a straight portion 106 of reduced width disposed in groove 105 within arcing chamber 94 which merges into a full-width curved portion 107 disposed adjacent stationary contact 49 within arcing compartment 89 and then is bent into a protruding straight terminal portion 108.

An L-shaped metallic bracket 109 (see FIG. 1) is aflixed to bus bar conductor 46 by screws, and a pair of spring contacts 110 mounted on bracket 109 by a rivet arc resiliently biased against each other and form a female connector. When arc chute housing 80 is assembled on contactor base 39, terminal portion 108 of arc runner 97 fits between spring contacts 110 to electrically connect arc runner 97 to bus bar conductor 46 and stationary contact 49.

Arc runner 98 has a straight portion 111 of reduced width disposed within groove 102 in side member 81 and exposed arcing chamber 93 which merges into a full width, bent-over portion 112 disposed both within said groove 102 and within groove 103 in side member 82 and exposed within arcing compartment 89 adjacent the path of movement of movable contact 21 and which is bent into a protruding, straight terminal portion 113. A pair of spring contacts 118 resiliently urged toward each other are secured by a rivet to support bracket 31 and form a female connector to receive terminal portion 113 of arc runner 98 and electrically connect arc runner 98 to movable contact 21 through flexible conductors 28.

The edges of arc splitter plate 92 are disposed against the vertical edges 120 and 121 of rims 83 and 84, and are splitter plate '92 is clamped against movement when side members 81 and 82 are assembled.

Bridging electrode 99 is of V-shape with the legs 123 and 124 disposed in different planes and on opposite sides of arc splitter plate 92 and with leg 123' disposed within elongated groove 101 in side member 81 and leg 124 disposed within groove 104 in side member 82. One pair of divergent electrodes is formed between leg 123 and portion 111 of arc runner 98 in arcing chamber 93, and another pair of divergent electrodes is formed between leg 124 and portion 106 of arc runner 97 in arcing chamber 94. The apex portion 126 of V-shaped bridging electrode 99 is disposed within arcing compartment 89 approximately midway between arc runners 97 and 98 and spaced slightly away from the path of movable contact 21.

A plurality of spaced arc splitter ridges, or vanes 127 molded on the interior of side members 81 and 82 abut against arc splitter plate 92 and divide the arc segments within each of the chambers 93 and 94 into a series of arclets, or arc streams as the arcs are forced outward within these chambers by the magnetic field between pole piece plates 62.

The edge 128 of side member '81 between rims 83 and the edge 129 of side member 82 between rims 84 diverge outwardly and define exhaust openings 130 for arcing chambers 93 and 94, and arc splitter plate 92 carries a V-shaped-in-cross section member 131 which partially defines such exhaust openings 130 and flares them in opposite directions to prevent the arcs in chambers 93 and 94 from combining.

In operation, when stationary and movable contacts 49 and 21 separate under overload conditions, an arc is formed therebetween which lengthens as the contacts separate. The magnetic field between pole pieces 62 is in a direction perpendicular to side members 81 and 82 and interacts with the current of the arc to lengthen it and force it to move from compartment 89 outward into arcing chambers 93 and 94. After partial separation of contacts 21 and 49, the arc transfers to portion 107 of arc runner 97 which is electrically connected to the stationary contact 49. Movable contact 21 is provided with a hook-shaped portion 132 which approaches the bentover portion 112 of arc runner 98 (which is electrically connected to the movable contact 21) and transfers the arc to runner 98 near the final travel of the opening movement of contact 21. As the ends, or roots of the arc are driven outward under the influence of the magnetic field, the arc jumps to the apex portion 126 of bridging electrode 99 and is split into two are segments, or arclets, by are splitter plate 92. Side members 81 and 82 have opposed inwardly curved surfaces 133 and 134 respectively which approach each other and together form a restricted entrace chute into arcing chamber 94 that is disposed to one side of arc splitter plate 92, thereby squeezing and decreasing the cross section of arc and increasing its resistance while simultaneously splitting the are into two are segments. Side members 81 and 82 also have opposed, inwardly curved surfaces 135 and 136 respectively which approach each other and together form a restricted entrance chute into arcing chamber 93 that is disposed to the opposite side of arc splitter plate 92, thereby decreasing the cross section of the arc and increasing its resistance. The curved surfaces 133, 134, 135 and 136 eliminate sharp edges and fiat surfaces where deionized gases can accumulate and thus aid in splitting the arc and forcing the arc segments through the restricted entrance chutes into arcing chambers 93 and 94. One arc segment is within arcing chamber 94 between arc runner 97 and leg 124 of bridging electrode 99 and is in series with the other arc segment in arcing chamber 93 between leg 123 of bridging electrode 99 and are runner 98. The pair of electrodes in each arcing chamber 93 and 94 diverge, and the magnetic field generated by blowout coil 54 is in a direction to cause the arc roots to continuously move outward along the divergent electrodes, thereby lengthening the arc and cooling it as it is driven outward. The continuous movement of the arc roots along the divergent electrodes avoids high heat concentration and vaporization of the metal of the arc runners and thereby minimizes the metallic content of the arc stream and reduces the stability of the arc to expedite interruption. The arc is split into two arc segments and reduced in cross section in being forced into the entrance chutes into the arcing chambers 93 and 94, and the arc segments in each of the chambers 93 and 94 is further subdivided into a plurality of arclets by the splitter ridges 127 as the arc segments approach the widest separation between the divergent electrodes. The lengthening of each arc segment and subdividing it into a series of shorter arcs rapidly dissipates the energy in the arc and increases the critical voltage of the series of arcs and eventually builds up suflicient arc voltage to effect extinction of the arc. The hot gas and deionized arc products are expelled in diverging directions through discharge ports 130.

Elongated grooves 140 formed in surfaces 133, 134, 135 and 136 increase the creep distance between the bridging electrode 99 and the arc runners 97 and 98.

The arc chute of the invention has almost twice the interrupting capacity of known structures without substantial increase in size. The blowout effect of coil 54 is greatly increased by splitting the are into two arc segments in side-by-side arc chambers 93 and 94 and causing the arc roots to continuously travel along divergent electrodes so they cannot vaporize the electrodes and so that each arc segment can be lengthened to the full extent allowed by the blowout coil 54 and the two arcs ruptured separately by the same blowout coil.

While only a single embodiment of the invention has been illustrated and described, many modifications and variations thereof will be readily apparent to those skilled in the art, and consequently it is intended in the appended claims to cover all such modifications and variations which are within the true spirit and scope of the invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An arc chute for a direct current contactor having a stationary contact and a movable contact, comprising a housing of electrically insulating material providing a contact receiving arcing compartment and first and second side-by-side arcing chambers in planes parallel to the plane of movement of said movable contact and also providing first and second restricted entrance openings from said contact receiving compartment into said first and second arcing chambers respectively, said housing having spaced side wall portions defining said compartment and an arc splitter wall portion disposed between and spaced from said side wall portions and together therewith defining said side-by-side arcing chambers, said compartment being substantially wider than said first and second arcing chambers in a direction transverse to said plane of movement of said movable contact and enclosing said stationary and movable contacts,

a generally V-shaped metallic bridging electrode having first and second legs respectively disposed on opposite sides of said arc splitter wall portion in said first and second arcing chambers and a bridging portion joining said legs disposed in said contact receiving compartment adjacent the path of movement of said movable contact,

a first elongated metallic arc runner disposed in said first arcing chamber in spaced and divergent V- shaped relation to said first leg of said bridging electrode and having an arc transfer portion disposed in said contact receiving compartment adjacent the path of said movable contact, and

a second elongated metallic arc runner disposed in said second arcing chamber in spaced and divergent V- shaped relation to said second leg of said-bridging electrode and having an arc transfer portion positioned in said contact receiving compartment adjacent said stationary contact,

said bridging portion of said bridging electrode being disposed within said contact receiving compartment between said are transfer portions of said first and second arc runners, said first entrance opening being formed by said housing between said bridging portion and said arc transfer portion of said first metallic runner in the plane of said first arcing chamber and said second entrance opening being formed between said bridging portion and said are transfer portion of said second metallic runner in the plane of said second arcing chamber.

2. An arc chute in accordance with claim 1 and including ferromagnetic pole piece plates on the exterior of said housing in planes parallel to said plane of movement of said movable contact.

3. An arc chute in accordance with claim 1 wherein said housing forms exhaust openings from said first and second arcing chambers opposite the widest separation between the divergent electrode pairs and which exhaust openings diverge relative to each other.

4. An arc chute in accordance with claim 3 wherein said housing has a plurality of spaced arc splitter wall means in each said arcing chamber for subdividing the arc segment formed therein between said bridging electrode and said are runner into a series of shorter arcs.

5. In the combination of claim 1 wherein said side wall portions of said housing have opposed smoothly and in- Wardly curved wall portions partially defining said contact-receiving compartment which approach each other to form said first and second entrance openings of reduced cross section which squeeze the are as it is forced from said compartment into said first and second arcing chambers.

6. In the combination of claim 5 wherein said smoothly curved wall portions which define said first and second entrance openings obstruct entry of the are into said first arcing chamber between said bridging portion of said bridging electrode and said are transfer portion of said second arcrunner and also obstruct entry of the arc into said second arcing chamber between said bridging portions and said are transfer portion of said 'first arc runner.

7. In the combination of claim 1 wherein said are chute is removable from said contactor and said first and second arc runners have terminal portions protruding from said housing and said contactor has first and second connector means releasably engaging said terminal portions for electrically connecting said first and second arc runners to said movable and stationary contacts respectively.

8. In the combination of claim 1 or 5 wherein said are chute is removable from said contactor and including complementary guide flange means and guide groove means for removably mounting said arc chute on said contactor, one of said guide means being on said are chute and the other of said guide means being on said contactor.

9. An arc chute in accordance with claim 1 or 5 where in said are transfer portions of said arc runners and said bridging portion of said bridging electrode extend across the entire width of said arcing compartment.

10. An arc chute in accordance with claims 1, 7 or 8 wherein said housing comprises a pair of insulating side members having protruding divergent peripheral rims in abutting relation and a thin insulating plate clamped between said side members defining said arc splitter wall portion and together with each side member forming a generally V-shaped arcing chamber having said entrance and exhaust openings respectively adjacent the narrowest and widest separation between said divergent rims, the opposed inner surfaces of said abutting side members also forming said contact-receiving compartment and said entrance openings from said compartment into said arcing chambers.

References Cited UNITED STATES PATENTS 2,861,152 11/1958 Scully. 3,155,801 11/1964 Pokorny 200-147 FOREIGN PATENTS 710,229 9/1941 Germany. 478,824 1/ 1938 Great Britain. 715,121 9/1954 Great Britain. 43 5,321 5/ 1948 Italy.

ROBERT S. MACON, Primary Examiner US. Cl. X.R. 200l47 

